This invention relates to an improved aluminum article. This invention also relates to a process for forming the improved aluminum article.
Aluminum articles having treated oxidized surfaces have become well known. The low friction and high corrosion resistance of their surfaces have made such aluminum articles very useful in industry. Aluminum articles having a thin layer of porous irregular coarsely crystalline aluminum oxide formed on their surfaces and a thin coating sealing the porous oxide have been particularly useful. This is because the coating has adhered very strongly and tenaciously to the aluminum substrate and has therefore been highly abrasion resistant. See, for example, U.S. Pat. Nos. 3,533,902 and 3,574,071.
However, the strength, hardness and corrosion resistance (e.g., salt water resistance) of such coated aluminum surfaces have not been considered adequate for many applications, for which the light weight and strength properties of aluminum and the low friction properties of such coated surfaces might otherwise be valuable, for example, in airplanes and in electrical power generating equipment. There has been a need, therefore, for a hard oxidized aluminum surface having enhanced strength, hardness and corrosion resistance properties better than heretofore known.